Facile Sol-Gel Synthesis, Structural Properties, and Characterization of Copper Titanate-Based Double Perovskites Modified with Lanthanides.

Abstract

In this work, a facile methodology was developed through a Sol-Gel process assisted by citric acid for the synthesis of mixed oxides Ln_2/3Cu₃Ti₄O₁₂ (Ln = La, Pr, Nd, Gd, Er, Tm, and Yb), and Ce_1/2Cu₃Ti₄O₁₂. The XRD diffractograms refined by the Rietveld method allowed the identification of the phases present in the samples. Morphological determination by HRTEM showed the presence of crystallographic planes related to an adopted A type double perovskite structure, while STEM provided an elemental mapping of the synthetized nanocrystals. Through FTIR-ATR spectroscopy, the impact of calcination temperature on the structures was identified, pointing out changes in the vibrational modes corresponding to citrate ions and organic compounds, and showing the formation of modes related to metal-oxygen bonds. This study allowed us to conclude that the appropriate calcination temperature is 1070°C, producing predominantly 90% of the double perovskite structure in most of the sequence of lanthanides studied, and to propose the sol-gel methodology as a scalable and commercially convenient route to produce type A cation-ordered double perovskites Ln_2/3Cu₃Ti₄O₁₂. Through Raman spectroscopy, the characteristic vibrational modes of the Ln_2/3Cu₃Ti₄O₁₂ double perovskite structure were studied. DFT calculations were performed for the Ce_1/2Cu₃Ti₄O₁₂ compound to compare theory with experimental results. The optical characterization allowed the determination of the bandgap of the samples.